This proposal will investigate candidate oncogene PDE4D in prostate cancer and explore the potential of a small molecule PDE4D inhibitor, NVP-ABE171, as an anti-prostate cancer agent. Our laboratory used a transposon-mutagenesis strategy to identify common transposon insertion sites that were recurrently mutated in mice with phenotypic changes resembling prostate cancer. One novel candidate gene that was identified was a phosphodiesterase called PDE4D. Preliminary data showed that PDE4D protein expression was increased in human prostate cancer cell lines and in human prostate cancer tissue. Finally, shRNA knockdown of exons common to all PDE4D isoforms reduced prostate cell proliferation and migration in prostate cancer cell lines and in xenograft-bearing mice. Analysis of alternative splicing of PDE4D identified one isoform of PDE4D, called PDE4D5v2, that was the predominant isoform found in human prostate cancer samples. This data suggested that PDE4D5v2 is a potential prostate cancer oncogene. The hypothesis of this proposal is that the up-regulation of isoform-specific PDE4D is critical for prostate cancer development, and the PDE4D inhibitor NVP-ABE171 will decrease the growth and/or progression of prostate cancer in pre- clinical models. In Aim 1, isoform specific knockdown of PDE4D5v2 with shRNA technology will be used to assess the impact of PDE4D5v2 on proliferation and signaling pathways important in prostate cancer. In Aim 2, the over-expression of PDE4D5v2 in human prostate cancer will be modeled in mice using a transgenic approach to drive expression of PDE4D5v2 specifically in prostatic epithelial cells. A cDNA for human PDE4D5v2 will be cloned into an expression construct that places PDE4D expression under the control of the ARR2PB version of the rat probasin promoter. The expression construct will be used to create transgenic mice with over-expression of PDE4D5v2 in the prostatic epithelium using pro-nuclear injection. Changes in the prostates of the ARR2PB-PDE4D5v2 transgenic mice that resemble features of human prostate cancer will be identified using histology and immunohistochemical approaches. In Aim 3, the PDE4D specific inhibitor, NVP- ABE171, will be tested for the ability to slow prostate cancer growth and/or progression first in prostate cancer cell lines and in xenografts of prostate cancer cell lines in nude mice, and finally for its ability to prevent and/or reverse the prostatic phenotypes caused by PDE4D5v2 over-expression in transgenic mice and in mice with prostate specific deletion of the tumor suppressor Pten. This research proposal is applicable to human health because it will define the role of a novel prostate cancer oncogene in the development of prostate cancer and will assess the efficacy of NVP-ABE171 as an anti-prostate cancer agent. The potential of NVP-ABE171 to be used in future clinical trials for prostate cancer is significant if the data can demonstrate efficacy in the pre-clinical models that I have proposed to study. PUBLIC HEALTH RELEVANCE: This proposal will explore a novel prostate cancer oncogene and will test the efficacy of a small molecule inhibitor of the novel oncogene. This inhibitor can be taken orally and extensive safety data is available for this class of drugs, making it an ideal potential anti-prostate cancer therapy. The potential of this inhibitor to be used in future clinical trials for prostate cancer is significant if the data can demonstrate efficacy in the pre- clinical models of prostate cancer that I have proposed to study.